Lady Bracknell: My nephew, you seem to be displaying signs of triviality. Jack: On the contrary, Aunt Augusta, I've now realised for the first time in my life the vital Importance of Being Earnest. (III.180-181)
Despite Jack’s statement that he’s learned the "Importance of Being Earnest" or the importance of being honest, we must question his sincerity. Because we realize that there is a pun between the adjective earnest and the proper name, Ernest, we can interpret Jack’s comment as tongue-in-cheek. He was accidentally truthful in telling Gwendolen his name was Ernest. But he was still untruthful about his younger brother being named Ernest. So in this way, Jack is both earnest and deceitful for the duration of the play. So what does Jack mean here? The importance of being honest? Or the importance of being named Ernest?